Prostate cancer (CaP) has become the most frequently diagnosed neoplasm and the second leading cause of cancer mortality in men second to lung cancer. Androgen-independent tumor growth accounts for the rapid progression of CaP following failure of primary androgen ablation therapy. whether a change in the molecular mechanism of androgen receptor (AR) function can contribute to the progression of human CaP to an androgen-independent state is an important question and will be the major goal of this proposal. It has been demonstrated that even though CaP becomes androgen-independent in advanced stages, with the immunohistochemical techniques, investigators can still detect the existence of AR in most of the CaP samples. In addition, in the human LNCaP cell line, Kokontis et al. demonstrated that the expression of AR at both the mRNA and protein levels rises when these cells are kept in a low androgen culture environment, which may mimic the clinical environment after androgen ablation therapies. As a result, these LNCaP 104-R cells become androgen hypersensitive in the regulation of target gene expression and their proliferation can be suppressed by a low level of supplemented androgen. A similar situation might account for the "Flutamide Withdrawal Syndrome" in CaP patients. These observations have led us to suspect that failure of expression of AR may account for only a small portion of patients with androgen-independent CaP and alteration of the function of AR could result in androgen-independent tumor progression. Hence, we propose several specific aims to test the following two hypotheses: Hypothesis l: We hypothesize that AR-associated proteins (ARAs) might form a complex with A-AR and result in the androgen-activation process. We propose that if the ARA proteins are absent or available in limited quantity cells, the existing AR may not function properly. We plan to use the yeast two-hybrid and far-Western hybridization systems to clone ARAs and characterize their roles in prostate androgen action. Hypothesis II: We propose that the alterations in LNCaP 104-R, LNCaP CSS5B, PC3AR7 and PCAR1O cell behavior may be the result of the change in AR to ARA ratio (based on our data that 1:3 ratio can maximize A-AR activity). To test this hypothesis, we plan to over-express the ARA candidate(s) from hypothesis l in these cells and follow any changes in cell response to androgen stimulation. If our hypothesis is correct, we will expect the cell behavior to revert to that of the original LNCaP cells, i.e., androgen stimulates cell proliferation. If this proves to be correct, then it will be possible (1) to design a diagnostic kit for ARA to monitor the status of CaP androgen dependency and (2) to develop therapeutic agents that induce more ARA expression in CaP to overcome androgen independence. As a result, ultimately, we might find a potential protocol to manage the progression of CaP in the clinic.